1. Field of the Invention
This invention relates to a manufacturing method and design of modularized leadframe, more specifically relates to pre-packaged leads, which can be used for selectively supplying a leadframe package semi-product or for further designing product with chip attached.
2. Description of the Related Art
As shown in FIG. 1, in conventional package structure, a semiconductor chip 10 is enclosed in a thermo-setting or ceramic material package body 20 to form a hermetic seal. Leads 30 (leadframe) on both sides of the semiconductor chip 10 extend out the package body 20 such that the bottom surface 301 of the leads 30 can be used as a soldering part connecting to the printed circuit board, but this package structure suffers a drawback of too bulky; therefore, another package technology emerges where leads are only exposed at the bottom surface of the package body as a soldering surface, as shown in FIG. 2, here a semiconductor chip 10′ is seated or attached on leads 30′, then an encapsulated body 20′ is used to enclose the structure to form a hermetic package, the bottom surface 301′ of the leads 30′ are exposed and in the same plane with the bottom surface of encapsulated body 20′, this surface 301′ can be used as a soldering part connecting to the printed circuit board, a further improvement on package size reduction can thus be obtained.
But the above-mentioned wholly-packaged semiconductor structure suffers a drawback that it can not arbitrarily select the wire-bonding methods or a wire-bonding operation can not be performed according to actual needs or it is impossible to change leads number after packaging, therefore this kind of product is less flexible. Furthermore, the bottom surface 301′ of the leads 30′ are exposed and in the same plane with the bottom surface of encapsulated body 20′, this easily leads to the penetration of encapsulated material 20′ into the bottom surface 301′ before it is solidified, which in turn form defective and need to be trimmed, production cost and quality control cost are thus increased. Moreover, normally chip has been packaged before it comes to assembly house, in addition, the assembly of semiconductor electronic components onto printed circuit board is in a sealing status, the above-mentioned packaging operation which uses expensive packaging material results in the difficulty of lowering packaging production cost.